Phenylbutyl isothiocyanate (PBITC) is an inhibitor of chemically-induced lung carcinogenesis [1]. n-Butyl thiophene (BT) inhibits colon carcinogenesis [2]. LKT laboratories has designed thienylbutyl isothiocyanate (TBITC) to incorporate the active functional groups of isothiocyanate in PBITC and thiophene in BT to achieve the inhibitory activities of both compounds. The activity of TBITC has been confirmed by three prescreening assays: the induction of glutathione-S-transferase, the inhibition of lung methylation, and reduction of colon aberrant crypts formation. Bioassays with lung and colon tumor models indicate that TBITC is an effective cancer chemopreventive agent in both target tissues. Structure activity relationship studies of phenylalkyl isothiocyanates have shown that there is a preference for longer alkyl chain lengths in the prevention of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)-induced lung tumors, with a six carbon chain being the most effective [3]. Against esophageal tumors induced by N-nitrosomethylamylamine (NMAA), an ethyl group is the most effective [4]. Benzyl isothiocyanate, but not phenylethyl isothiocyanate, inhibits benzo[a]pyrene-induced lung tumors [5]. LKT offers the full series from thienylmethyl isothiocyanate (n=1) to thienyl decyl isothiocyanate (n=10), plus thienyl dodecyl isothocyanate (n=12).